1. Field of the Invention
This invention relates to rotary kilns for the treatment of a tumbling bed of mixed-size pulverulent material and particularly to ports in the kiln shell for discharging gases such as fuel, steam and/or air to the interior of a rotary kiln wherein the port is self-purging of the pulverulent material.
2. Description of the Prior Art
In the prior art, rotary kilns are known wherein a plurality of ports are provided through the shell of the kiln to admit air and fuel into the interior of the kiln. Examples of such prior art kiln are disclosed in U.S. Pat. Nos. 1,216,667; 2,091,850 and 3,182,980. Nozzles for such kilns are disclosed in U.S. Pat. Nos. 3,794,483; 3,946,949 and 4,214,707. Mechanisms for operating such nozzles are disclosed in U.S. Pat. Nos. 3,847,538 and 4,070,149.
In certain of the prior art, e.g., U.S. Pat. Nos. 1,216,667 and 2,091,850 kiln fuel and/or air is injected into the kiln through ports while the ports are below the material charge of the bed. In the other of the aforesaid prior patents, air and such, as a fuel gas, is injected alternately with the fuel gas being injected when the ports are beneath the bed of the material charge and air being injected when the ports are over the bed. With the aforesaid apparatus operated to process mixed size materials, the smaller particles may enter the ports and associated piping impairing the flow of fluid through the ports and eventually causing complete clogging of the ports, rendering it useless for under bed fluid injection.
Additionally, while such rotary kilns may have as many as 600 nozzles, commonly five or more of the nozzles are activated by a single valve. Consequently, if material particles enter the associated piping through any one port and damage a valve, numerous ports will become inoperative. This is particularly troublesome where a port is normally inactive and makes numerous passes beneath a bed of material with no gas passing through the port or associated piping. Thus, when a port or number of ports become useless by reason of being plugged or damaged to an associated control valve, the capacity of the kiln is reduced and its operational time span between maintenance periods is reduced.
Ports have been proposed which prevent particulate material from entering port piping. U.S. Pat. No. 4,214,707 to Flaherty dated July 19, 1980 discloses a self-purging port for a rotary kiln. In the Flaherty patent, the port has a nozzle having a plurality of orifices for passing fluid to the interior of a kiln. Behind the nozzle is a labyrinth trap. Particulates from the kiln are allowed to pass through the nozzle orifices into the trap as the port passes beneath material in the kiln. A plurality of orifices in the trap causes fluid to swirl as the fluid passes through the trap on its way to the interior of the kiln. This swirling causes the fluid to pick up the particulates in the trap and carry them into the kiln.
The aforementioned copending and commonly assigned patent application of Peter J. Petit and Thomas J. Gill, filed concurrently herewith, discloses a port comprising a nozzle and a base member cooperating to define a particle screening mechanism to prevent particles from entering the port pipe, or port sleeve.
While the above-mentioned ports act to prevent particulate material from entering the associated port pipe, some of the very smallest particulate material will eventually elude the aforementioned screening mechanisms and pass into piping. Even the smallest amount of material, however, is potentially damaging to valves which regulate the ports.
It is a general object of the present invention to provide a further improved port construction, which purges particulate material, which may pass the port screening mechanism and enter the port piping.